This invention relates generally to an apparatus for suspending a pipe within a well casing. More particularly, it relates to improvements in which the pipe is suspended within the casing by slips spaced equally about a body and adapted to be raised over a conical surface thereabout for expansion radially outwardly into gripping engagement with the casing.
It is known that, in the design of a slip, a compromise must be made between slips of shallow taper and large taperxe2x80x94i.e., small or large angles between their cylindrical and conical surfaces. Although desirable from the standpoint of spreading radial loads on the pipe and casing, the shallow tapers increase the radial loads on the pipe and casing, and thus increase the possibility of collapsing the pipe and/or bursting the casing.
It is also known to reduce radial loading by means of xe2x80x9ccontrolled frictionxe2x80x9d due to blunt teeth formed on the sides of the slips opposite the teeth for galling the surface over which the slips are slidable.
It is further known to reduce radial loading by means of slip assemblies of such construction as to exert circumferential loads on the body in order to mimic radial loads. An improved apparatus and method is desired for suspending a pipe within a well casing.
According to the primary object of this invention, each of the slips is of such design that it combines desirable features of all three concepts so as to minimize the risk of collapsing the pipe and/or bursting the casin
It is a further object to provide a slip assembly of such construction that although the pipe and casing would ordinarily be subjected to radial loading due to the shallow taper of the slips, these loads are minimized by both controlled friction and circumferential loading.
These and other objects are accomplished, in accordance with an illustrative and preferred embodiment, by apparatus in which a tubular body from which the pipe is suspended is adapted to be lowered into the bore of the casing so as to suspend the pipe therein has longitudinally extending, equally spaced pockets disposed about and concentric with the outer circumference of the body with each pocket having an open face, side walls, and upper and lower end walls. A cone is adapted to be installed within each pocket beneath the upper wall thereof and has an inner cylindrical surface concentric with the body, a downwardly and inwardly extending outer conical surface, and opposite side edges engaging side walls of the pockets. A slip having teeth on its outer side has an inner conical surface concentric with the outer conical surface of each cone for sliding upwardly and vertically with respect thereto. The inner and outer sides of each slip form a relatively small vertical angle with respect to one another, preferably in the range of 2-4 degrees.
Each side wall of each pocket has a slot adjacent to and extending parallel to the outer conical surface of each cone when in the pocket, and a rib is provided on each lateral side of each slip for fitting closely within a slot as the slip is lowered into the pocket for landing on lower end wall of the pocket so as to retain the cone and slip within the pocket. The slip may be raised over the cone by means of a tie bar having a vertical actuator, for sliding upwardly over the outer conical surface of the cone, to cause the slip teeth to grip the casing and thus suspend the pipe within the casing as the weight of the pipe is slacked off. A tight fit of the side edges of the cone within the side walls of the pocket cause the load to be transmitted to the body in a circumferential direction, and thus as loop loading. The inner side of each slip has relatively blunt teeth for galling the outer side of the adjacent cone when the teeth on the outer side of the slip have engaged the bore of the casing and the weight of the pipe is slacked off onto the casing.